To be consistent I use TIF files which where created by corrected DNG files in Lightroom. Transforming the files is very time- and space consuming. Does anybody has experiences with using DNG files with Helicon? Does the final result looks the same as with Tif-Files? Does Helicon convert the DNG Files as Lightroom with all the corrections?

Helicon Focus can open DNG files but corrections made by Lightroom will not be taken into account. I personally would stack DNG files and applied color corrections to stacked result only. If color changes are moderate, it is not important if they are made before or after stacking.